Prompt and error-free repair of critical genomic alterations of toxicant exposures is vital to normal survival of living organisms. During the previous project period, we have shown that global genomic repair lends itself to elaborate regulatory control for orchestrating the "comings and goings" of multiple repair factors. This continuation project will extend the scope of these studies along a similar overall theme. The proposal is based on the premise that in response to genotoxin exposures, several seemingly independent cellular pathways converge to function in tandem for the distinctive recognition and effective excision of DNA lesions. The specific hypotheses addressed are: (i) entire repair edifice is composed from the initial regulated attaching of DNA damage binding protein that impinges on recruiting subsequent core repair factors, (ii) cellular ubiquitin/proteasome apparatus intimately participates in sequential clearance of repair factors that are tightly bound to damage sites, and (iii) the involved repair protein complexes allow bridging between diverse pathways through multi-acting pleiotropic factors. The specific aims will focus on: (1) establishing the biochemical/molecular basis for selective damage recognition and recruitment of DDB containing E3 Ub-ligase complex to diverse DNA lesions, (2) defining the role of Ub-mediated proteolysis in lesion hand-over during repair processing, (3) delineating the nature and function of DNA damage dependent XPC modifications, (4) establishing the molecular basis for differential role of hHR23A/B in regulation of XPC ubiquitination/degradation and UV-induced p53 response, and (5) understanding the role of 19S proteasomal components and other cellular deubiquitinating enzymes in regulation of XPC stability. The experimental studies will continue to concentrate on genomic modifications induced by a representative physical (UV radiation) and a chemical (anti-BPDE) genotoxic carcinogens and human cell lines representing multiple organ systems, e.g., skin fibroblast, liver hepatocytes, breast and lung epithelium. State-of-the-art biochemical, molecular and cellular methodologies, mostly established in the PI's laboratory, will be applied along with the newer evolving technologies to accomplish these specific objectives. The studies will provide seminal insights into the molecular responses of xenobiotic action and processing of resultant genotoxic damage which has crucial implication in risk assessment of human environmental exposures.